The present invention relates to a Gamma-correction circuit. More particularly, the present invention relates to using varistors, transistors, or operation amplifiers in a Gamma-correction circuit to obtain an adjustable based Gamma-correction circuit with central-symmetry voltage.
In an active matrix liquid-crystal-display (AM-LCD) system, the character curve, which shows the transmittance of the liquid crystals versus the applied driving voltage in FIG. 1, is a non-linear curve. In order to obtain a linear character curve or special relation curve with the best vision effect for human eyes between transmittance of the liquid crystals and the code number, as shown in FIG. 2. The relationship between the driving voltages and the code numbers should be determined, so that the linear character curve or special relation curve with the best vision effect for human eyes between transmittance of the liquid crystals and the code number can be obtained. As shown in FIG. 3, the curve, which all the code numbers can be mapped into the specific driving voltages, is called Gamma curve.
In the AM-LCD system, the main function of the Gamma-correction circuit is to make reference to the Gamma curve for transferring the code numbers to the corresponding driving voltages, and then the driving voltages can be applied to the liquid crystals of the AM-LCD system. By using the Gamma curve, the intensity, gray level, contrast, and color performance of the LCD can be adjusted. Therefore, the Gamma curve, which is determined by the Gamma-correction circuit, is very important in the color quality of the LCD.
In the generality of cases, if the more driving reference voltages are applied by the Gamma-correction circuit, the less approximating errors to the Gamma curve can be obtained. Under the requirement of the high color performance of the display, 256 code numbers of 8-bit data should be provided, and 256 code numbers mean that the display can provide 256 gray levels. It is the optimum that 256 reference voltage sources are provided by an adjustable circuit, but it is impossible to do this. Furthermore, because the nematic liquid-crystal has the character of AC driving, 512 driving voltages, which comprise 256 plus driving reference voltages and 256 minus driving reference voltages, should be applied to the Gamma-correction circuit. Referring to FIG. 4, a conventional Gamma-correction circuit is shown. Two voltages (Vn and Vnxe2x88x921) are provided between a plurality of serial resistors (R1xcx9cRm). By adjusting the resistor value, each driving voltage (VR1xcx9cVRmxe2x88x921) between these two voltages (Vn and Vnxe2x88x921) can be obtained at each node. As shown in FIG. 1, each node is connected to a buffer, so that the output of the buffer is the driving voltage. In this way, the input voltages can be decreased by using the dividing voltage of the serial resistors.
In the AC driving circuit, as shown in FIG. 5, two input reference voltage terminals (Vcc and VGnd) are serially connected a plurality of symmetrical resistor (R1xcx9cRm), and then the open ends of these two resistors (Rm) are connected to each other for forming a central voltage node. In this way, the Gamma-correction circuit has the central voltage ((Vcc+VGnd)/2), and symmetrical driving voltages (+V1, xe2x88x92V1, +V2, xe2x88x92V2xcx9c+Vmxe2x88x921, xe2x88x92Vmxe2x88x921) based on the central voltage. Using the conventional Gamma-correction circuit, it is very easy to obtain the driving voltages. However, it is very difficult to obtain the symmetrical driving voltages and the central voltage when they need to be adjusted, because all the driving voltages will be affected when one of the serial resistors is changed. Furthermore, the non-symmetrical driving voltages will induce the flicker phenomena of image, and make the poor image quality.
Due to the requirement of the high color performance of the display, it is necessary to have an exact Gamma curve. In order to approximate the Gamma curve, the number of the driving reference voltages should be increased. Therefore, a Gamma-correction circuit, which can generate the most adjustable driving reference voltages by using the minimum voltage sources, is necessary.
It is therefore an object of this invention to provide an adjustable based Gamma-correction circuit with central-symmetry voltage. The present invention provides varistors, transistors, or operation amplifiers in a Gamma-correction circuit to obtain a plurality of plus and minus symmetrical driving voltages based on a central voltage.
It is another object of this invention to provide an adjustable based Gamma-correction circuit with central-symmetry voltage. Utilizing the present invention, a Gamma-correction circuit can generate the most adjustable driving voltages by using the minimum voltage sources.
In accordance with all aspects of this invention, the invention provides an adjustable based Gamma-correction circuit, comprising: a plurality of symmetrical dividing voltage units, each symmetrical dividing voltage unit including a serial connection of a first resistor, a resistor value control circuit, and a second resistor between a first input terminal and a second input terminal, an input of a first buffer connected at a first end of the resistor value control circuit, and an input of a second buffer connected at a second end of the resistor value control circuit for respectively generating a pair of the plus driving voltage and the minus driving voltage from an output of the first buffer and an output of the second buffer, and wherein the output of the first buffer and the output of the second buffer of each symmetrical dividing voltage unit are respectively connected to the first input terminal and the second input terminal of the next symmetrical dividiespectively connected to a first voltage and a second voltage.
In accordance with all aspects of this invention, this invention provides an adjustable based Gamma-correction circuit, comprising: a plurality of symmetrical dividing voltage units, each symmetrical dividing voltage unit including a varitor having a drawing terminal connected between an input terminal and a first voltage, a first amplifier having the drawing terminal connected to a plus input of the first amplifier and a minus input of the first amplifier connected to an output of the first amplifier, a second amplifier having a first resistor connected between the minus input of the first amplifier and a minus input of the second amplifier and a second resistor connected between the minus input of the second amplifier and an output of the second amplifier and the central voltage connected to a plus input of the second amplifier for respectively generating a pair of the plus driving voltage and the minus driving voltage from the output of the first amplifier and the output of the second amplifier, and wherein the output of the first amplifier of each symmetrical dividing voltage unit is connected to the input terminal of the next symmetrical dividing voltage unit, and the first input terminal is connected to a second voltage.